function SetToFloor()
{
var altitude;
temp.x=my.x;
temp.y=my.y;
temp.z=my.z;
vec_set(temp2,temp);
temp2.z=-4000;
trace_mode= ignore_me + ignore_you + use_box + IGNORE_PASSABLE + IGNORE_MODELS ;
trace(temp,temp2);
altitude=target.z-10;
my.z=altitude;
my.shadow = on; //If you want it to have it's own shadow.
my.material=mat_wood;
my.ambient=85;
mat_model.albedo = 2;

}

It might need a bit of changes to you own likenings, just place this functions on the models you want to be set to floor.